This invention relates to a method of restoring an original picture with high density through estimation in the field of facsimile or in a copying machine.
A method is known in the art in which, where a picture to be sampled (or an original picture) is divided into square picture elements in the form of a grid, which are all sampled to restore through estimation curves or the like indicated white and black, if the aimed picture element is white (or black), white (or black) minute picture elements obtained by dividing the aimed picture element into four equal parts is changed into black (or white) minute picture elements (cf. Japanese Patent Laid-Open No. 41115/1978).
In the conventional picture restoring method, the original picture sampled with low density is restored with high density, thereby to reproduce especially the curves with high fidelity. However, even if the sampling is effected with 4 picture elements/mm.times.4 picture elements/mm and the restoration is performed with 8 picture elements/mm.times.8 picture elements/mm, i.e. the restoration is effected with 2-fold density according to the conventional method, the picture element density is still insufficient. That is, the conventional method cannot sufficiently reproduce the curves, and the restored picture is still insufficient in resolution.